The invention relates to novel polycarbodiimide-based block copolymers, a method of preparing them and also their use as hydrolysis stabilizers in ester-group-containing polymers.
Organic carbodiimides are known. Their chemistry and their preparation are described, for example, in Chemical Reviews, vol. 81 (1981), pages 589 to 639 and Angewandte Chemie 74 (1962), pages 801 to 806.
Monocarbodiimides and oligomeric polycarbodiimides can be prepared, for example, by the action of basic catalysts on mono- or polyisocyanates. Suitable as basic catalysts are, for example, heterocyclic, phosphorous-containing compounds in accordance with GB-A-1 083 410 and phospholenes and phospholidines as specified in DE-B-11 30 594 and also their oxides and sulfides.
Furthermore, polycarbodiimides having terminal urethane groups are described, for example, in U.S. Pat. No. 2,941,983 and DE-B-22 48 751. The products can be prepared, for example, by carbodiimidization of diisocyanates with sterically hindered isocyanate groups and subsequent partial or complete urethanation of the terminal NCO groups with alcohols. As described in DE-A-2 248 751, if aromatic diisocyanates having isocyanate groups with different reactivity are used, the isocyanate groups having higher reactivity with alcohol may be partially or completely converted into the corresponding urethane groups and the remaining isocyanate groups may be reacted to form carbodiimide groups with the elimination of carbon dioxide.
The carbodiimides and polycarbodiimides are preferably used as stabilizers to prevent the hydrolytic cleavage of polyester-based plastics. According to the specifications of DE-A-14 94 009, aromatic and/or cycloaliphatic monocarbo-diimides, in particular, are suitable for this purpose that are substituted in position 2 and 2xe2x80x2, such as 2,2xe2x80x2,6,6xe2x80x2-tetraisopropyidiphenylcarbodiimide. Polycarbodiimides having a molecular weight of over 500 and a content of more than 3 carbodiimide groups are described in DE-B-12 85 747 as stabilizers to counteract the effects of heat and moisture in ester-group-containing plastics.
Although a substantial stability of ester-group-containing plastics with respect to moist heat, water and water vapor can be achieved by adding said (poly)carbodiimides as stabilizers, the products also have disadvantages. A disadvantage of the tetraalkyl-substituted monocarbodiimides, such as, for example, 2,2xe2x80x2,6,6xe2x80x2-tetraisopropyldiphenylcarbodiimide, preferably used industrially, is their relatively high vapor pressure and their tendency as a result of the low molecular weight to migrate out of the polyaddition products, for example thermoplastic polyurethanes (TPU) or polycondensation products, for example polyterephthalates. To eliminate this deficiency, according to the specifications of EP-A-0 460 481, substituted monocarbodiimides or oligomeric substituted polycarbodiimides having terminal isocyanate groups are used which are prepared from substituted diisocyanates and that virtually do not release toxic volatile substances originating from the carbodiimides used either when hot, for example under the conventional processing conditions, or at room temperature. Polycarbodiimides of this type have higher melting points or cannot be melted and can be introduced into the polyurethanes and/or their parent substances only with an appreciable expenditure in terms of apparatus and time. The distribution of the polycarbodiimides in the ester-group-containing plastics is, therefore, often insufficiently homogeneous so that the stabilizer action does not meet the expectations.
More readily melting polycarbodiimide derivatives can be obtained by converting some of the terminal isocyanate groups into urethane groups, for example in accordance with DE-A-22 48 751 or U.S. Pat. No. 2,941,983.
Because of the statistical occurrence of monocarbodiimides and short-chain homologues, there is also in these compounds the tendency to form cleavage products that have low vapor pressure and a high tendency to migrate in the plastic and that tend to outgas at the higher processing temperatures.
In polymers that are incapable of forming hydrogen bridge bonds, such as polyesters and polycarbonates, the terminally masked urethane groups bring about incompatibility effects that limit their effectiveness.
The object of the present invention was to eliminate the above-mentioned disadvantages entirely or at least partly and to provide hydrolysis protection agents that have a high efficiency at low dosage in ester-group-containing polymers, that are nontoxic, that have a high thermal stability, that do not release toxic cleavage products when exposed to heat and that have good compatibility with the polymer matrix and do not therefore, effloresce out of the ester-group-containing polymers.
Surprisingly, this object was achieved by using polycarbodiimide-based block copolymers of formula (I)
Xxe2x80x94[xe2x80x94(A)mxe2x80x94(B)nxe2x80x94]oxe2x80x94Xxe2x80x83xe2x80x83(I), 
in which
X is identical or different and is selected from xe2x80x94NHCOxe2x80x94R, xe2x80x94NHCONHxe2x80x94R, xe2x80x94NHCOOxe2x80x94R, xe2x80x94NHCOSxe2x80x94R, xe2x80x94COOxe2x80x94R, xe2x80x94Oxe2x80x94R, xe2x80x94NR2, xe2x80x94Sxe2x80x94R, xe2x80x94OH, xe2x80x94NH2, xe2x80x94NHR, Sxe2x80x94H, and xe2x80x94NCO, but preferably stands for xe2x80x94NHCONHxe2x80x94R, xe2x80x94NHCOOxe2x80x94R, xe2x80x94OH, and wherein the group R denote an alkyl, cycloalkyl, aralkyl or aryl radical containing 1 to 30, preferably 2 to 18, carbon atoms,
m, n are, independently of one another an integer from 1 to 1000, preferably from 5 to 200,
o is an integer from 1 to 500, preferably from 3 to 100,
A is selected from the carbodiimides or polycarbodiimides of formula (II)
xe2x80x94(xe2x80x94Nxe2x95x90Cxe2x95x90Nxe2x80x94Yxe2x80x94)xe2x80x94xe2x80x83xe2x80x83(II), 
xe2x80x83in which
Y is selected from ortho- or bisortho-substituted aromatics, aralkylenes in which the carbon atom linked to the carbodiimide group is substituted by C1- to C14-alkyl groups, and cycloalkylenes in which the carbon atom linked to the carbodiimide group is substituted by C1- to C14-alkyl groups, and
B is selected from the group comprising (poly)dioles, (poly)diamines, (poly)dimercaptans, (poly)aminoalcohols, (poly)aminomercaptans and (poly)mercaptoalcohols.
The invention furthermore provides a method of preparing the block copolymers according to the invention and the use of the block copolymers according to the invention as stabilizers to prevent the hydrolytic degradation of ester-group-containing polymers.
To prepare the polycarbodiimides (component A, formula II) incorporated in the block copolymers according to the invention of formula (I), diisocyanates can be condensed as starting compounds at elevated temperatures, for example at 40 to 200xc2x0 C., in the presence of catalysts with the release of carbon dioxide. Suitable methods are described in DE-A-11 30 594. Strong bases or phosphorous compounds, for example, have proved satisfactory as catalysts. Phospholene oxides, phospholidines and phospholine oxides are preferably used. Suitable for preparing the component A according to the invention are all diisocyanates, wherein aromatic diisocyanates substituted by C1- to C4-alkyl, such as 2,4,6-triisopropylphenyl 1,3-diisocyanate, 2,4,6-triethylphenyl 1,3-diisocyanate or 2,4,6-trimethylphenyl 1,3-diisocyanate, substituted diisocyanatodiphenyl-methanes, such as 2,4xe2x80x2-diisocyanato-diphenylmethane, 3,3xe2x80x2,5,5xe2x80x2-tetraisopropyl-4,4xe2x80x2-diisocyanatodiphenylmethane or 3,3xe2x80x2,5,5xe2x80x2-tetraethyl-4,4xe2x80x2-diisocyanatodiphenylmethane and substituted aralkyls, such as 1,3-bis(1-methyl-1-isocyanatoethyl) benzene, are preferably used. These diisocyanates can be used individually or as mixtures to prepare component A of formula (I).
The degree of polymerization or degree of condensation, respectively, m in the formula (I) can be adjusted by the choice of reaction conditions, such as reaction temperature, reaction time and amount of catalyst. This can easily be tracked by determining the NCO content or by the carbon dioxide evolved. Preferably, the degree of condensation is adjusted so that residual isocyanates in the range from 1 to 8 wt. % are still present in the polycarbodiimide (component A).
Dioles, diamines, dimercaptans, aminoalcohols, aminomercaptans, mercaptoalcohols or their polymerization products and mixtures thereof can be used as component B of the block copolymer (I) according to the present invention. Preferred dioles are 1,2-ethanediol, 1,4-butanediol, 2,2-bis(4-hydroxyphenyl)propane, poly(ether dioles) based on ethylene glycol, propylene glycol and tetramethylene glycol and mixtures thereof, poly(ester dioles) based on adipic acid, ethylene glycol, propylene glycol, butanediol and/or tetramethylene glycol, poly(ester dioles) based on ethylene glycol and phosphoric acid, dioles derived from polyolefins, for example from ethylene/butylene polymers. In particular, mention is made of, poly(ester dioles) based on adipic acid and ethane diole and poly(ether dioles) based on ethylene glycol or propylene glycol having a mean molecular weight in the range from 300 to 10,000 g/mol.
Preferred diamines are hexamethylenediamines, ethylenediamine and poly(ether amines) prepared by terminating polyethers with amines. Mention is made of poly(ether amines) based on propylene glycol and/or ethylene glycol having a mean molecular weight of 300 to 10,000 g/mol.
Preferred dimercaptans are 1,6-hexanedithiol, 1,12-dodecyldithiol, 1,18-octadecyidithiol and polyether/polydisulfides, so-called thiocols, having a mean molecular weight of 500 to 10,000 g/mol.
The preparation of the cited compounds of component B is generally known. Thus, for example, the synthesis of poly(ether dioles) is described in Kunststoff-Handbuch, vol. 7, 3rd edition (1993), Hanser-Verlag, pages 58-65, and the synthesis of poly(ester dioles) is described in Kunststoff-Handbuch, vol. 7, 3rd edition (1993), Hanser-Verlag, pages 67-71. The dioles mentioned therein are therefore the subject matter of the present invention.
The block copolymers according to the present invention are prepared by copolymerization of the two starting components A and B. In principle, the known polymerization methods, such as free-radical polymerization, cationic polymerization, anionic polymerization, polycondensation or polyaddition, can be used for this purpose. The block copolymers according to the present invention are preferably prepared by means of polyaddition of diisocyanates with dioles to form polyurethanes or with diamines to form polyureas, as described in Kunststoff-Handbuch, vol. 7, 3rd edition (1993), Hanser-Verlag, pages 11-15. For this purpose, residual-isocyanates-containing polycarbodiimides of component A are reacted with terminal functional groups, i.e. amines or alcohols, at elevated temperature using a catalyst. The reaction temperature is in this case 30xc2x0 to 200xc2x0 C. The common polyurethane catalysts, for example tin(II) compounds, tin(IV) compounds or tertiary amines, such as those described in Kunststoff-Handbuch, vol. 7, 3rd edition (1993), Hanser-Verlag, pages 104-110 can be used as catalyst. Dibutyltin dilaurate and/or triethylenediamine in concentrations of approximately 0.05 to 1 wt. % have proven to be particularly suitable.
The molar mass and, consequently, the degree of polymerization o and the terminal groups of the block copolymers according to the present invention can be adjusted by means of the stoichiometric composition. Preferred is a molar ratio of component A to component B in the range (0.7 to 1.3):1, in particular from (0.90 to 1.10):1.
The reaction of the two components can be performed in reactors typical of chemistry. Particularly suitable as reactors are stirred tanks, compounders, 2-component mixers, such as those described in Kunststoff-Handbuch vol. 7, 3rd edition (1993), Hanser-Verlag, pages 143-147, and extruders.
The block copolymers produced in the reaction according to the present invention of components A and B still contain reactive terminal groups, such as isocyanate, amino, hydroxyl and mercapto groups, which can be reacted by common chemical methods with suitable functionalized alkyl, cycloalkyl, aralkyl or aral compounds containing 1 to 30 carbon atoms, preferably 2 to 18 carbon atoms, to form the desired end group X in formula (I).
The block copolymers according to the present invention of formula (I) have a mean molecular weight of approximately 1000 to 100,000 g/mol.
The block copolymers according to the present invention are eminently suitable as acid scavengers, in particular of organic acids, and are consequently preferably used as stabilizers to prevent the hydrolytic degradation of ester-group-containing polymers. In this connection, the group of polymers comprises both polycondensation products, for example polyesters, polyamides, polycaprolactones, polyester amides, polyether imides and polyether esters, and also polyaddition products, for example polyurethanes, polyureas and polyurea/polyurethane elastomers and free-radical prepared polymers, for example polyvinyl acetate and native polymers, for example, derivatives of cellulose and starch, in particular cellulose lactate.
The concentration of the block copolymers according to the present invention in the ester-group-containing polymers to be stabilized is, in general, 0.01 to 15 wt. %, preferably 0.1 to 5 wt. %, relative to the total mixture. In individual cases where the polymer is particularly stressed, the concentration may also be higher.
The block copolymers according to the present invention can be introduced into the ester-group-containing polymers to be stabilized by various methods. For example, the block copolymers according to the present invention can be blended with one of the educts that are used to prepare the polymers, for example the isocyanates or the polyols, or the block copolymers can be added directly to the reaction mixture during the preparation of the polyurethanes. Furthermore, the block copolymers according to the present invention can be added to the melt of the polymers in the final stage of reaction. According to a further procedure, the block copolymers according to the present invention can also be predispersed in a carrier material, such as, for example, thermoplastic molding compositions, in order subsequently to add these master batches present, as a rule, in solid granules to the final application.